Peripheral Nervous System Flashcards
What are peripheral nerves composed of?
bundles of axons
What are the types of peripheral nerves?
- sensory (afferent)
- motor (efferent)
- autonomic (also motor)
What do autonomic nerves do?
they are motor nerves that are involved in functions that are NOT under voluntary control
What does the efferent autonomic nerve pathway consist of?
two-neuron chain between CNS and effector organ
- 1st neuron: preganglionic
- 2nd neuron: postganglionic
Motor Neurons
What do motor neurons innervate?
striated muscle fibres
Motor Neurons
Where are motor neurons located?
cell body (soma) is in CNS
Motor Neurons
What do motor neurons do?
release acetylcholine – acts via nicotinic receptors at neuromuscular junction (NMJ)
Sensory Neurons
Where are sensory neurons located?
cell body (soma) is outside CNS in sensory ganglia (in PNS)
What is a ganglion?
collection of neuronal cell bodies in PNS
Autonomic Neurons
Where are autonomic neurons?
in PNS
Autonomic Neurons
What are the 2 types of autonomic neurons?
sympathetic
parasympathetic
Autonomic Neurons
Where is the 1st neuron (preganglionic) in the efferent autonotmic nerve pathway?
cell body is in CNS
Autonomic Neurons
Where is the 2nd neuron (postganglionic) in the efferent autonotmic nerve pathway?
in autonomic ganglion in periphery
- sympathetic system: ganglion is close to CNS in sympathetic system
- parasympathetic system: ganglion is close to, or actually within, the target organ
What are the functions of the autonomic nervous system (ANS)?
- homeostasis – maintaining stable internal environment
- controls vegetative systems (life support) – semi-autonomously, and coordinates with endocrine systems
- blood pressure – HR, stroke volume, total peripheral resistance
- GI motility
- salt/water balance
- pupillary reflexes
- sexual function
What is the ANS coordinated via? (4)
- some reflexes at spinal cord level
- medulla (within brainstem)
- hypothalamus
- prefrontal cortex – emotional states
What do ANS afferent do?
send information into control centres
ANS Afferents
What are baroreceptors?
type of mechanoreceptors allowing for relaying info derived from blood pressure within ANS – monitors blood pressure
ANS Afferents
Where are baroreceptors located?
in aortic arch and carotid sinus
ANS Afferents
What do osmoreceptors do?
regulation of plasma ions
ANS Afferents
Where are thermal receptors located?
in skin and CNS
ANS Afferents
What do thermal sensors do?
regulate body temperature
ANS Afferents
What do cutaneous receptors do?
detect sexual stimuli
ANS Afferents
What do stretch receptors do?
monitor distention in lungs, bladder, stomach, bowel
ANS Afferents
What are 6 types of ANS afferents?
- baroreceptors
- osmoreceptors
- thermal sensors
- cutaneous receptors
- pain fibres in viscera
- stretch receptors
Describe the structure of the sympathetic nervous system.
- has short cholinergic preganglionic fibres
- has long adrenergic postganglionic fibres
What does cholinergic mean?
releases acetylcholine
What does adrenergic mean?
releases norepinephrine
Where does the sympathetic nervous system originate?
thoracolumbar regions of spinal cord
Describe the structure of the parasympathetic nervous system.
has long cholinergic postganglionic fibres
Where does the parasympathetic nervous system originate?
in brain and sacral region of spinal cord
Do sympathetic and parasympathetic nerve fibres innervate the same thing?
usually, they both innervate the same effector organs
What is the adrenal medulla?
modified sympathetic ganglion that releases epinephrine and norepinephrine into blood
What are the catabolic effects of the sympathetic nervous system? (4)
- increased heart rate, stroke volume, and blood pressure
- increased blood flow to skeletal muscle
- decreased blood flow to skin
- fight or flight response
What are the anabolic effects of parasympathetic nervous system? (4)
- decreased heart rate, stroke volume, and blood pressure
- increased GI tract motility and secretions
- relaxation of sphincters in esophagus, stomach, bladder
- paradoxical co-activation
What happens in the fight or flight response?
release of epinephrine/norepinephrine from adrenal medulla stimulates skeletal muscle glycogenolysis
What is paradoxical co-activation?
both sympathetic and parasympathetic systems activated during intense conflict situations
Cranial Nerves
Where do cranial nerves originate?
inside cranium and proximal spinal cord
Cranial Nerves
What can cranial nerves carry? (3)
- afferent information (fibres)
- efferent fibres
- ANS fibres
Cranial Nerves
How many cranial nerves are there?
12 pairs
Cranial Nerves
What are the 12 pairs of cranial nerves?
I - olfactory II - optic III - oculomotor IV - trochlear V - trigeminal VI - abducens VII - facial VIII - auditory (vestibulocochlear) IX - glossopharyngeal X - vagus XI - accessory XII - hypoglossal
Cranial Nerves
Which cranial nerves are involved in swallowing?
IX, X, and XI
vagus (X) is most important
Cranial Nerves
Olfactory (I)
- type
- function
type: sensory
function: smell
Cranial Nerves
Optic (II)
- type
- function
type: sensory
function: vision
Cranial Nerves
Oculomotor (III)
- type (2)
- function (2)
type: motor, voluntary
function: moves eyeball medially (towards midline)
type: motor, autonomic (parasympathetic)
function: constricts pupil and thickens lens
Cranial Nerves
Trochlear (IV)
- type
- function
type: motor, voluntary
function: moves eyeball
Cranial Nerves
Trigeminal (V)
- type (2)
- function (2)
type: motor, voluntary
function: mastication
type: sensory
function: touch, temperature, pain (ie. from face, head, and mouth)
Cranial Nerves
Abducens (VI)
- type
- function
type: motor
function: moves eyeball laterally
Cranial Nerves
Facial (VII)
- type (3)
- function (3)
type: motor, voluntary
function: muscles of facial expression
type: motor, autonomic (parasympathetic)
function: lacrimal and salivary glands
type: sensory
function: taste buds of anterior ⅔ of tongue
Cranial Nerves
Auditory/Vestibulocochlear (VIII)
- type (2)
- function (2)
type: sensory
function: (from cochlea) hearing
type: sensory
function: (from vestibular apparatus) gravity, motion, and position of head
Cranial Nerves
Glossopharyngeal (IX)
- type (5)
- function (5)
type: motor, voluntary
function: pharynx swallowing
- ———————————–
type: motor, autonomic (parasympathetic)
function: salivary glands
- ———————————–
type: sensory
function: taste buds of posterior ⅓ of tongue
- ———————————–
type: sensory
function: carotid sinus baroreceptors
- ———————————–
type: sensory
function: carotid body chemoreceptors
Cranial Nerves
Vagus (X)
- type (4)
- function (4)
type: motor, voluntary
function: pharynx swallowing and larynx phonation
- ———————————–
type: motor, autonomic (parasympathetic)
function: (heart (slows heart rate) to abdominal organs) controls secretion and motility
- ———————————–
type: sensory
function: aortic baroreceptors and chemoreceptors
- ———————————–
type: sensory
function: GI tract
Cranial Nerves
Accessory (XI)
- type (2)
- function (2)
type: motor, voluntary
function: swallowing
type: motor, voluntary
function: shoulder shrugging
Cranial Nerves
Hypoglossal (XII)
- type
- function
type: motor, voluntary
function: tongue
Cranial Nerves
Which two cranial nerves have opposing functions? Do they work together?
oculomotor (III): moves eyeball medially
abducens (VI): moves eyeball laterally
must work together when we are looking right or left
Cranial Nerves
How do cranial nerves III and VI coordinate?
by information carried in medial longitudinal fasciculus (MLF) – tract connecting III nerve nucleus to VI nerve nucleus
What do carotid sinus baroreceptors do?
- monitors pressure of arterial blood
- important in reflex regulation of heart rate and BP
What do carotid body chemoreceptors do?
- monitors CO2, O2 in arterial blood
- important in control of breathing
How many spinal nerves are there?
31 pairs
What are the functions of spinal nerves?
- all have voluntary motor function
- all (except C1) have sensory fibres
What are the 5 types of spinal nerves and how many are there?
8 cervical (C1-C8) 12 thoracic (T1-T12) 5 lumbar (L1-L5) 5 sacral (S1-S5) 1 coccygeal
Where do sympathetic fibres arise from?
???
all thoracic, and 1st and 2nd lumbar segments (T1-L2)
Where does sympathetic innervation of the head come from?
upper thoracic spinal nerves
- none of the cranial nerves carry sympathetic fibres
Where are parasympathetic fibres?
???
cranial nerves III, VII, IX, and X, and S2-S4
Where do parasympathetic preganglionics arise from?
???
S2-S4
